When an array is created that is too large, return QualType() instead of a valid type.

[rsmith]

lib/Sema/SemaType.cpp

1564–1567

How about just returning QualType() here? An invalid type should do a better job of suppressing follow-on diagnostics than an array-of-unexpected-size.

[rtrieu]

lib/Sema/SemaType.cpp

1564–1567

Returning QualType() also would prevent the crash, however it also causes a new error to be emitted. "initializer element is not a compile-time constant" on __builtin_offsetof(struct Chunk2, data).

[rtrieu]

When a too large array is requested, use QualType() to indicate there is not a valid type being created.

[rsmith]

LGTM

[rtrieu]

Committed in r181970.

lib/Sema/SemaType.cpp

virtual void diagnoseFold(Sema &S, SourceLocation Loc, SourceRange SR) {
       S.Diag(Loc, diag::ext_vla_folded_to_constant) << SR;
     }
   } Diagnoser;
 
   return S.VerifyIntegerConstantExpression(ArraySize, &SizeVal, Diagnoser,
                                            S.LangOpts.GNUMode).isInvalid();
 }
 
+/// Set NumElements to the max size that an array of ElementType can be,
+/// using MaxBits addressing.
+static void getMaxArraySize(ASTContext &Context, QualType ElementType,
+                            unsigned MaxBits, llvm::APSInt &NumElements) {
+  uint64_t ElementSize = Context.getTypeSizeInChars(ElementType).getQuantity();
+  llvm::APInt ElementSizeInt(MaxBits, ElementSize);
+  NumElements = llvm::APInt::getAllOnesValue(MaxBits).udiv(ElementSizeInt);
+}
 
 /// \brief Build an array type.
 ///
 /// \param T The type of each element in the array.
 ///
 /// \param ASM C99 array size modifier (e.g., '*', 'static').
 ///
 /// \param ArraySize Expression describing the size of the array.
if (ConstVal == 0) {
           << ArraySize->getSourceRange();
         ASM = ArrayType::Normal;
       }
     } else if (!T->isDependentType() && !T->isVariablyModifiedType() &&
                !T->isIncompleteType()) {
       // Is the array too large?
       unsigned ActiveSizeBits
         = ConstantArrayType::getNumAddressingBits(Context, T, ConstVal);
-      if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context))
+      if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context)) {
         Diag(ArraySize->getLocStart(), diag::err_array_too_large)
           << ConstVal.toString(10)
           << ArraySize->getSourceRange();
+        // Set array size to largest allowable size.
+        getMaxArraySize(Context, T, ConstantArrayType::getMaxSizeBits(Context),
+                        ConstVal);
+      }
     }
 
     T = Context.getConstantArrayType(T, ConstVal, ASM, Quals);
   }
 
   // OpenCL v1.2 s6.9.d: variable length arrays are not supported.
   if (getLangOpts().OpenCL && T->isVariableArrayType()) {
     Diag(Loc, diag::err_opencl_vla);

test/Sema/offsetof-64.c

 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-linux-gnu
-// expected-no-diagnostics
 
 // PR15216
 // Don't crash when taking computing the offset of structs with large arrays.
 const unsigned long Size = (1l << 62);
 
-struct Chunk {
+struct Chunk1 {
   char padding[Size];
   char more_padding[1][Size];
   char data;
 };
 
-int test1 = __builtin_offsetof(struct Chunk, data);
+int test1 = __builtin_offsetof(struct Chunk1, data);
 
+struct Chunk2 {
+  char padding[Size][Size][Size];  // expected-error 2{{array is too large}}
+  char data;
+};
+
+int test2 = __builtin_offsetof(struct Chunk2, data);